Define audio/summary_test as medium size (#559)
Define audio/summary_test as medium size (#559)

This broke the internal CI by taking longer than sixty seconds.
A test that spawns subprocesses also probably can't be called
small, according to the go/testsizes definitions.
tensorflow/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,qiuminxu/tensorboard,agrubb/tensorboard,francoisluus/tensorboard-supervise,francoisluus/tensorboard-supervise,tensorflow/tensorboard,agrubb/tensorboard,qiuminxu/tensorboard,tensorflow/tensorboard,agrubb/tensorboard,tensorflow/tensorboard,tensorflow/tensorboard,francoisluus/tensorboard-supervise,agrubb/tensorboard,agrubb/tensorboard,francoisluus/tensorboard-supervise,agrubb/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard,qiuminxu/tensorboard,francoisluus/tensorboard-supervise,tensorflow/tensorboard